Police who finally entered James Holmes' booby-trapped apartment, found over 30 homemade grenades and 10 gallons of gasoline, CNN reported.
Authorities believe the apartment was rigged to explode and harm whoever entered as soon as Holmes' door was opened.
"Imagine that fireball…you would have an explosion that would knock down the wall of (nearby) apartments. That flame would have consumed the entire third floor (of the apartment complex)," the official said, CNN reported. "By the time a fire truck would have arrived," the building would have been engulfed in flames.
Holmes, 24, was taken into custody in a parking lot behind the movie theater where he allegedly shot 70 people, at least 12 of them fatally, early Friday morning during a screening of "The Dark Knight Rises."
Police who attempted to enter the apartment over the weekend found that it contained dozens of home-made booby-traps constructed from liquid explosives, chemical, powders and bullets, the Washington Post reported.
Whoever planted them apparently wanted to "kill and maim any first responders or anyone that came in there," a law enforcement official said to the paper.
According to CNN, the grenades were wired to a control box in the kitchen. It was disabled by bomb technicians with the help of a remote-controlled robot that squirted water on it. It has been sent to Quantico, Virginia, for forensic analysis at the FBI laboratory, the official said.
Meanwhile, at least three people have been arrested across the United States for Dark Knight-related threats, the Washington Post reported.